Energy Savings Opportunity Scheme (ESOS)

Your organisation must comply if, on the qualification date of 31 December 2026, it meets the definition of a large undertaking. This means you either: 

• Employ 250 or more people, OR 

• Have an annual turnover exceeding £44 million AND an annual balance sheet totalling more than £38 million 

Important: If your organisation is part of a corporate group that includes at least one large UK undertaking, you must also comply with ESOS Phase 4, even if your individual entity doesn't meet the above criteria. 

Mandatory Action Plan Progress Reporting 

For the first time, you must provide evidence of progress against the energy-saving opportunities identified in your Phase 3 Action Plan. If commitments were not met, a clear explanation must be included in your Phase 4 assessment. 

Removal of Compliance Routes 

Display Energy Certificates (DECs) and Green Deal Assessments (GDAs) are no longer accepted as valid routes to compliance. 

Net Zero Alignment 

While mandatory net-zero reporting has been delayed until Phase 5, the Environment Agency are encouraging organisations to voluntarily align with the new PAS 51215 standards to future-proof your compliance strategy. 

• Qualification Date: 31 December 2026 

• Compliance Period: 6 December 2023 to 5 December 2027 

• Compliance Deadline: 5 December 2027 

Your energy data and audits must cover the four-year compliance period and your completed ESOS notification must be submitted to the Environment Agency by the compliance deadline. 

Our lead assessors will guide you through the following steps: 

1. Calculate total energy consumption across your organisation

2. Identify areas of significant energy consumption (covering at least 95% of total energy use)

3. Calculate energy intensity ratios to benchmark performance

4. Determine compliance route(s) and confirm lead assessor appointment 

5. Conduct ESOS energy audits of significant energy use 

6. Complete the ESOS report and share findings with your corporate group 

7. Submit notification to the Environment Agency via their online portal 

8. Develop an Action Plan and commit to annual progress reporting 

Yes. You must appoint a qualified ESOS Lead Assessor to oversee and sign off your ESOS assessment, unless your organisation is fully covered by ISO 50001 certification. 

We strongly recommend engaging a lead assessor early to allow adequate time for: 

• Energy data collection and validation 

• Site visits and audit activities 

• Report preparation and review 

• Avoiding the last-minute rush before the December 2027 deadline 

You can begin your ESOS Phase 4 audit now. While the compliance deadline is 5 December 2027, early preparation offers significant advantages: 

• More time for thorough data collection 

• Better availability for site visits 

• Opportunity to implement quick wins before the deadline 

• Reduced stress as the deadline approaches 

• Ability to spread costs over a longer period 

The duration varies depending on several factors: 

• Size and complexity of your organisation 

• Number of sites requiring audits 

• Availability and quality of energy data 

• Ease of site access 

At Optopia, we typically complete most ESOS audits within 1-2 months from project commencement, though larger or more complex organisations may require additional time. Early engagement helps ensure a smooth, efficient process. 

Non-compliance carries serious consequences: 

• Initial fine: Up to £50,000 

• Daily penalties: £500 per day for continued non-compliance (up to £40,000) 

• Public naming: Non-compliant organisations are published on the Environment Agency's register 

Important: Even after paying penalties, you will still be required to complete a full ESOS audit to achieve compliance. 

Your complete ESOS report remains confidential and is not published. However, certain elements submitted to the Environment Agency are made public, including: 

• Corporate information and structure 

• Actual performance metrics and energy consumption data 

• Energy reduction achievements since ESOS Phase 2 (December 2019 onwards) 

• Estimated savings identified during your Phase 3 audit 

• Potential energy-saving opportunities from Phase 4 

This transparency is designed to encourage accountability and drive sector-wide improvement in energy efficiency. 

• Expert guidance throughout the entire ESOS process 

• Data collection assistance to ensure accuracy and completeness 

• Comprehensive energy audits tailored to your organisation 

• Actionable recommendations that deliver real energy and cost savings 

• Support with Environment Agency notification and submission 

• Action Plan development to help you capitalise on identified opportunities